Temperature-stable and low loss Fe-containing dielectrics in BaO-Ln 2 O 3 -Fe 2 O 3 -Ta 2 O 5 system Liang Fang • Zhao Yang • Hui Zhang • Chunchun Li • Xiyang Peng • Changzheng Hu • Dongjin Chu Received: 1 November 2010 / Accepted: 13 December 2010 / Published online: 9 January 2011 Ó Springer Science+Business Media, LLC 2011 Abstract Polycrystalline samples of Ba 4 Ln 2 Fe 2 Ta 8 O 30 (Ln = La and Nd) were prepared by a high temperature solid-state reaction technique. The formation, structure, dielectric and ferroelectric properties of the compounds were studied. Both compounds are found to be paraelec- trics with filled tetragonal tungsten bronze (TB) structure at room temperature. Dielectric measurements revealed that the present ceramics have exceptional temperature stabil- ity, a relatively small temperature coefficient of dielectric constant (s e ) of -25 and -58 ppm/°C, with a high dielectric constant of 118 and 96 together with a low dielectric loss of 1.2 9 10 -3 and 2.8 9 10 -3 (at 1 MHz) for Ba 4 La 2 Fe 2 Ta 8 O 30 and Ba 4 Nd 2 Fe 2 Ta 8 O 30 , respectively. The measured dielectric properties indicate that both mate- rials are possible candidates for the fabrication of discrete multilayer capacitors in microelectronic technology. 1 Introduction Some niobates and tantalates with TB structure have received increasing interests because of their great potential in dielectric and ferroelectric applications [1, 2]. The tungsten–bronze structure consists of a complex array of distorted BO6 octahedral sharing corners in such a way that three different types of interstices (A1, A2, and C) are available for cation occupying in the general formula (A1) 2 (A2) 4 (C) 4 (B1) 2 (B2) 8 O 30 [1]. Generally, the smallest interstice C is empty, so the general formula is A 6 B 10 O 30 for the filled tungsten–bronze structure. Because of the com- plex crystal structure, the physical properties of tungsten– bronze structure could be modified in wide scale and are complicated and interesting. According to some recent work, most of the tungsten–bronze tantalates are paraelec- trics at room temperature [3–5], while the tungsten–bronze niobates generally indicate ferroelectric or relaxor ferro- electric nature [6–8]. Recently, the tungsten–bronze tanta- lates containing rare-earth elements Ln (Ln = La, Nd, and Sm), have been widely investigated with view to search for temperature stable dielectrics. Chen et al. also reported the presence of dielectric materials with the filled TB structure with high dielectric constant (103 * 175) and low dielec- tric loss (10 -4 –10 -3 at 1 MHz) in the BaO-Ln 2 O 3 -TiO 2 - Ta 2 O 5 quaternary system [3]. However, the large negative temperature coefficients of dielectric constant (s e )(-728 to -2,500 ppm/°C) preclude the practical application. Several methods have been used to reduce the s e value of the TB ceramics, such as ionic substitution to form solid solution and addition of a secondary phase with the opposite s e value. Fang et al. have proposed some relatively tempera- ture stable dielectric ceramics such as Ba 5 LnZnTa 9 O 30 [5], and Ba 5 LnNiTa 9O30 (Ln = La, Nd and Sm) [9] through Zn 2? or Ni 2? substituting Ti 4? at B-sites. The temperature stability of Ba 4 Nd 2 Ti 4 Ta 6 O 30 ceramics were also modified through Bi, Sr and Ti substitutions for Nd, Ba and Ta at A and B-site, respectively [10]. However, these ionic substi- tutions lead to a limited decrease in s e value. Meanwhile, temperature stability was achieved for Ba 5 NdTi 3 Ta 7 O 30 ceramic by introducing a secondary phase Bi 4 Ti 3 O 12 , but L. Fang  Z. Yang  H. Zhang  C. Li  X. Peng  C. Hu  D. Chu State Key Laboratory Breeding Base of Nonferrous Metals and Specific Materials Processing, Guilin University of Technology, 541004 Guilin, People’s Republic of China L. Fang (&)  Z. Yang  C. Li  X. Peng  C. Hu  D. Chu Key Laboratory of Nonferrous Materials and New Processing Technology, Ministry of Education, Guilin University of Technology, 541004 Guilin, People’s Republic of China e-mail: fangliangskl@yahoo.com.cn 123 J Mater Sci: Mater Electron (2011) 22:1208–1212 DOI 10.1007/s10854-010-0286-5